Crankcase drilling Question

olympus · May 2, 2018

Hi Guys
Plug tapping all the crankcase threads (timing case) I need to understand why the hole is treaded in the oil way return from the pressure relief valve through casing to oil pipe junction???.... was this originally used as a cover securing position....

Many thanks

comnoz · May 2, 2018

Some years the engines returned the pressure relief oil to the timing chest instead or the oil pump inlet. When using that style of side cover, the hole in the main case can be plugged with a socket head setscrew.
No Commando ever used that hole for attaching the side cover.

L.A.B. · May 2, 2018

olympus said:
Plug tapping all the crankcase threads (timing case) I need to understand why the hole is treaded in the oil way return from the pressure relief valve through casing to oil pipe junction???.... was this originally used as a cover securing position.....

On Commandos from '68 to '74 oil from the OPRV is sent back to the inlet side of the feed pump through the drilling, so unless a Mk3 or modified timing cover is used (where the OPRV vents into the timing chest) then DO NOT blank off the gallery.
The case drilling is threaded so a timing cover screw can be temporarily inserted whenever the timing cover is removed to prevent the contents of the oil tank from draining.

olympus · May 2, 2018

Blown away with the wealth of knowledge... many thank L.A.B

Kvinnhering · May 2, 2018

L.A.B. said:
On Commandos from '68 to '74 oil from the OPRV is sent back to the inlet side of the feed pump through the drilling, so unless a Mk3 or modified timing cover is used (where the OPRV vents into the timing chest) then DO NOT blank off the gallery.
The case drilling is threaded so a timing cover screw can be temporarily inserted whenever the timing cover is removed to prevent the contents of the oil tank from draining.

Is this pluging smart to do on a rebuilt or not?

olympus · May 2, 2018

What are the benefit/ reasoning to having the relief valve oil returned to the timing chest rather than into the inlet/pick up

olympus · May 2, 2018

I do a fair amount of work with hydraulic system, and introducing PRV oil into gravity pick ups is an absolute No No....
Oil is returned directly to reservoir... or in the case of later Commandos into timing chest for scavenging back to reservoir

L.A.B. · May 2, 2018

Kvinnhering said:
Is this pluging smart to do on a rebuilt or not?

olympus said:
What are the benefit/ reasoning to having the relief valve oil returned to the timing chest rather than into the inlet/pick up

It removes the possibility of oil draining (or 'wet sumping' if you like) through (or along the thread of) the OPRV.

olympus · May 7, 2018

If the existing hole is plugged and a new drilling made to exit the oil into the timing chest, are any additional holes required to allow the excess oil to return into the crankcase??

comnoz · May 7, 2018

No extra holes necessary. And the mod to dump the oil into the timing chest is a good move.
Early engines dumped the oil into the timing chest. I think it was only 73 and 74 engines that dumped the oil back to the inlet of the pump. [maybe 72?]
Since the oil tank is higher than the oil pump it doesn't cause a big problem but running the oil round and round in a loop does cause the oil to get hot. At least that is what I was told was the reason to go back to the earlier system on the 75 and later engine. I suspect it also slows wet sumping.

L.A.B. · May 8, 2018

comnoz said:
Early engines dumped the oil into the timing chest. I think it was only 73 and 74 engines that dumped the oil back to the inlet of the pump. [maybe 72?]

All Commando engines '68-'74.

olympus · May 8, 2018

Thanks guys. Does anyone have photos of hole position, angle & Drill diameter??
Many thanks

L.A.B. · May 8, 2018

https://www.accessnorton.com/Norton...valve-and-amr-modification.18868/#post-281850

PeterJoe · May 8, 2018

olympus said:
Thanks guys. Does anyone have photos of hole position, angle & Drill diameter??
Many thanks

Here is a link with a couple of my pictures from the thread that L.A.B. directed you to. Unfortunately I should have fixed that thread before it was too late.

https://www.accessnorton.com/Norton...-pressure-relief-valve-mod.24205/#post-356456

The hole that I drilled is 1/4 inch diameter and the angle is not at all important. You just don't want to drill up into the threaded area of the oil pressure relief valve. I used a 90 degree angle drill with a short drill bit to be able to drill in this location. As a matter of fact you could just notch the gasket surface area of the timing cover and get the same results.

While recovering from my Achilles tendon surgeries it has been 1 1/2 years since I have been able to ride my motorcycle. So I was really able to test the AMR modification along with my modification. It appears that the oil level hasn't dropped at all in the oil tank. I think it was well worth the modifications.

Peter Joe

olympus · May 9, 2018

Nice one Joe many thanks
Trust your up & well very soon

Crankcase drilling Question

olympus

comnoz

L.A.B.

Moderator

olympus

Kvinnhering

olympus

olympus

L.A.B.

Moderator

olympus

comnoz

L.A.B.

Moderator

olympus

L.A.B.

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PeterJoe

olympus

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